Positron emission tomography (PET) allows detection of cancer and heart disease. PET is considered a functional imaging method, because PET images can show the concentration of a radiotracer in different regions of the imaged organ over the course of time. The radiotracer is injected into the patient at a known location (e.g., the aorta). Sensors (e.g., silicon photomultipliers, SiPM) detect annihilation of positron pairs at various locations over time. The annihilation events indicate the blood flow and radiotracer uptake in the tissue of interest.
Compared to spatial anatomic images (e.g., computed tomography, CT or magnetic resonance imagery, MRI), PET images have lower spatial resolution, lower signal to noise ratio, and can appear more blurry. Also, PET images are captured over a longer period of time, and may have artifacts due to patient motion. As a result, the boundaries between organs in CT and MR images are sharper than PET images.
Many medical imaging systems incorporate spatial information from CT or MR imaging into PET image reconstruction to better define anatomical boundaries and improve image quality.